A.F. Gualtieri,     Università di Modena e Reggio Emilia, Italy

7.1 Introduction

Asbestos minerals have been known and used for millennia (Skinner et al., 1988). There is evidence that white asbestos (serpentine asbestos or chrysotile) was discovered and utilized for the first time in Cyprus, perhaps as long as 5000 years ago, for manufacture of cremation cloths, lamp wicks, hats, and shoes (Dilek and Newcomb, 2003). It was clear from the beginning that asbestos was a unique natural product, considered somehow magic, with outstanding physical, chemical and technological properties (especially incombustibility), usable for an endless number of applications in everyday life. The history of asbestos from classical times to the industrial age can be appreciated in Skinner et al. (1988) and Dilek and Newcomb (2003).

The modern asbestos industrial age began in the 1870 s with the opening of large asbestos industries in Scotland, Germany and England for the production of asbestos boards. Active mining in Quebec (Canada) began in 1878 and by 1885 seven white asbestos mines close to the town of Thetford were active. In 1896 the first asbestos brake linings were made by Ferodo Ltd in England. In 1907 brown (amphibole amosite, an acronym of ‘Asbestos Mines of South Africa’) asbestos was discovered in Transvaal (South Africa) and mined. Mining and production of blue (amphibole crocidolite) asbestos began near the town of Koegas (South Africa) in 1926. Mining of anthophyllite (amphibole) asbestos started in 1918 in Paakkila, eastern Finland. Chrysotile and tremolite (amphibole) asbestos from the Italian Alps were first exploited in Roman times but it was not until the early 1800 s, when manufacture of asbestos threads, paper and fabrics was perfected, that the alpine deposits (especially the Balangero mine in the Lanzo valley near Torino) became economically important (Dilek and Newcomb, 2003). It is not a surprise that the first asbestos pipes were developed in Italy in 1913.

For the reasons described in section 7.3, asbestos minerals are considered carcinogenic substances and their use is consequently restricted or banned by national laws in 55 out of the 195 countries (28%) of the world (see www.ibasecretariat.org). In the other countries worldwide, asbestos is exploited and used. The 2009 asbestos trade data (from the United States Geological Service) reported that the top five asbestos producers (t/year) in decreasing order are Russia (1,000,000), China (380,000), Brazil (288,000), Kazakhstan (230,000), and Canada (150,000). The top five asbestos users (t/year) in decreasing order are China (565,313), India (340,544), Russia (276,820), Brazil (140,272), and Thailand (102,738). In the countries where asbestos is banned, it has been progressively removed from the environment and eventually substituted by synthetic fibres. The most common substitute materials are inorganic fibres which are divided in two classes: man-made mineral fibres (MMMF) and man-made vitreous fibres (MMVF).

7.2 Classification of asbestos and mineral fibres, their structure, microstructure and properties

The term ‘asbestos’, from the Greek ἅσβεστoϛ or asbestinon which means ‘unquenchable’ or ‘inextinguishable’, was used in the beginning to describe any of the several fibrous minerals and usually those found as concentrated aggregates or in veins amenable to mining (Skinner et al., 1988). The nomenclature we now apply was coined in Germany in the eighteenth century and refers to minerals that occur as bundles of flexible fibres that can be separated into thin, durable threads. Frayed ends observed on a fibrous particle (Fig. 7.1(a)) indicate that it is composed of smaller fibrillar components, usually referred to as fibrils (Skinner et al., 1988). This peculiar crystal habit is called fibrous-asbestiform. The length of a single fibril usually ranges from a few microns up to decimetres. The outer diameter is in the range 10–50 nm whereas the inner diameter is in the range 1–10 nm. The length of a fibre usually ranges from a few microns to decimetres, whereas the diameter is usually less 0.5 μm. Stoichiometric chrysotile tubular nanocrystals (length in the range 200–500 nm and outer diameter in the range 20–50 nm) have also been synthesized as possible starting materials for applications towards nanotechnology (Falini et al., 2004).

Asbestos minerals are divided into two major groups: serpentine asbestos and amphibole asbestos. The fibrous-asbestiform variety of serpentine is called chrysotile. Chrysotile is the most commonly used form of asbestos. The amphibole asbestos family includes five minerals: actinolite, tremolite, anthophyllite, crocidolite (a fibrous variety of riebeckite), and amosite (a fibrous variety of grunerite). With respect to chrysotile, amphibole asbestos fibres are more brittle and usually exhibit a straighter, more needle-like crystal habit (Fig. 7.1(b)). The chemical composition of the six asbestos minerals together with their crystal symmetry are reported in Table 7.1.

Chrysotile and amphibole asbestos are both silicates sharing the same fibrous-asbestiform crystal habit but very different structural units at a molecular scale. The way nature assembles the different molecular units to realize similar output at macroscopic scale is very elegant. Chrysotile is a layer silicate composed of Si-centred tetrahedral (T) sheets in a pseudohexagonal network joined to Mg-centred octahedral (O) sheets in units with a 1:1 (TO) ratio (Fig. 7.2(a)). Since the TO unit is polar and a misfit exists between the smaller parameters of the T sheet and the larger ones of the O sheet (Bailey, 1988), a differential strain occurs between the two sides of the layer. The strain is released by rolling the TO layer around the fibril axis, which is usually the crystallograpic a axis (clinochrysotile and orthochrysotile) and more rarely the crystallographic b axis (parachrysotile). The fibrils are thus composed of concentrically or spirally curved layers, forming a tubular structure (Yada, 1971). By this mechanism, a layer silicate assumes a fibrous crystal habit (see Fig. 7.2(b)). Because the layers cannot energetically withstand too tight a curvature, the rolls possess hollow cores with a diameter of about 5–8 nm (Cressey et al., 1994). The earlier X-ray diffraction studies on chrysotile showed a remarkable distortion (curvature) of the unit cell with respect to the conventional crystal structures, so that a new theory specially formulated for cylindrical lattices was developed (Whittaker, 1956; Jagodzinski and Bagchi, 1953; Devouard and Baronnet, 1995).

Amphiboles are double-chain silicates with a Si(Al):O ratio of 4:11 (Fig. 7.2(c)) and the oxygen atoms of the chains coordinated not only to Si(Al) but to a variety of other cation sites, yielding the following simplified general formula (Veblen, 1981):

where T = tetrahedral sites within the silicate chain; C = fairly regular octahedral cation sites; B = less regular octahedral or eight-fold coordinated cation sites; and A = irregular cation sites having coordination in the range 6 to 12. Generally, in the rock forming amphiboles A = Na^+, K⁺; B = Na⁺, Li⁺, Ca^2 +, Mn^2 +, Fe^2 +, Mg^2 +; C = Mg^2 +, Fe^2 +, Mn^2 +, Al^3 +, Fe^3 +, Ti^3 +, Ti^4 +; and T = Si^4 +, Al^3 +. Because of the presence of strong bonds, amphiboles normally crystallize along the crystallographic c axis (Ferraris, 2002). Hence, the fibrous crystal habit is due to the monodimensional character of their structural units (chains).

Both serpentine and amphibole asbestos minerals display outstanding properties which have been exploited for the development of building materials. The main chemical-physical and technological properties of the commercial chrysotile, amosite and crocidolite asbestos minerals are ilustrated in Table 7.2.

In those countries where asbestos is banned, asbestos substitute materials are eventually used in building materials, the most common being synthetic inorganic fibres belonging to two distinct classes: man-made mineral fibres (MMMF) and man-made vitreous fibres (MMVF).

Some methods of classification of non-asbestos fibres have emphasized the origin (e.g., natural vs. man made) while others are based on their chemistry (e.g. inorganic vs. organic), structure, physical/technological properties or field(s) of application. Table 7.3 shows a general classification scheme of natural and man-made fibres (modified from Gualtieri et al., 2009a). The term man-made is designated to distinguish natural fibres (erionite or mordenite, wollastonite, and others) from synthetic ones. The MMMF group includes polycrystalline fibres whereas fibres belonging to the MMVF group are amorphous. MMVF are often referred to as silicate-based glass fibres, as the largest volume of MMVFs produced worldwide is of this type. However, in addition to fibreglass and fused silica, there are other amorphous fibres used in commerce. Some examples are alumina and silica combinations, rock and slag wool, as well as fibres with non-silicate compositions such as carbon. The dimensions (i.e. length, diameter, and length to diameter ratio) of the fibres are used to distinguish between continuous fibres, discontinuous fibres, and wools. Fibres with diameters > 3 μm are generally regarded as non-breathable and, therefore, cannot present an inhalation hazard (Vu, 1994).

Most of the non-asbestos fibres that are widely used in commerce today belong to the man-made ‘vitreous silicate’ category. However, the lack of a conclusive mode of classification of fibres in this group has permitted the use of the commercial terms fibreglass (glass wool), rock wool, slag wool and ceramic fibre (CF). The rock and slag wool products typically contain high amounts of calcium and magnesium oxides and are sometimes referred to as alkaline earth silicate glasses. CFs which contain higher concentrations of alumina are also called alumino-silicate glasses. The European Community recently introduced new definitions to describe MMVFs in order to amend Annex I of European Council Directive 67/548/EEC for the classification, packaging and labelling of dangerous substances. The directive subdivided ‘vitreous silicate fibres’ into ‘mineral wools’, which are understood to include glass, stone, rock and slag wools, and ‘refractory ceramic (RCF) and special purpose fibres’. The differentiation of these two categories, according to the European Community Directive, is based on the concentration of certain alkali and alkaline earth oxides (i.e. Na₂O, K₂O, CaO, MgO, and BaO). Fibres containing > 18 wt% and ≤ 18 wt% of these oxides belong to the first and second category, respectively. The sum of the alkali and alkaline earth oxides (as defined above), denoted here by the symbol Z, is presumably related to the potential hazard posed by exposure to these fibres. Fibres with Z values greater than 18 (i.e. mineral wools) are believed to be less hazardous than those for which the value of Z is less than 18 (i.e. RCF and special-purpose fibres). For all these fibres, the EC scheme provides another test that relies on the in vivo measurement of biopersistence (see, for example, Mast et al., 2000; Maxim et al., 1999) and Commission Directive 97/69/EC of 5 December 1997 defines the circumstances under which certain fibres must be labelled as carcinogens based on biopersistence.

7.3 Health effects of asbestos minerals

Worldwide, the number of workers passing away each year in asbestos-related cancer is estimated to be 100,000–140,000 (asbestos pandemia). In Western Europe, North America, Japan and Australia, 20,000 cases of diagnosed lung cancer and 10,000 cases of mesothelioma result every year from exposures to asbestos (Tossavainen, 2000).

The first evidence of the potential health hazard of asbestos minerals was reported at a time when these minerals were massively used in society. The history of the epidemiological reports of asbestos-related diseases is well described in Skinner et al. (1988) and will not be reported here.

Although many epidemiological studies since the early 1980s have provided convincing evidence that amphibole asbestos crocidolite and tremolite are clearly more dangerous than chrysotile asbestos (Hodgson and Darnton, 2000), all six asbestos minerals (chrysotile, actinolite, amosite, anthophyllite, crocidolite, and tremolite) have been assumed to be equally harmful to human health. This assumption was made for regulatory purposes.

Research into the toxicity of asbestos, initially performed to understand why the inhalation of asbestos had such devastating effects on health (Mossman et al., 1990), became relevant to the investigation of possible hazards from other fibres and led to the so-called fibre paradigm (Miller et al., 1999). The fibrogenicity and carcinogenicity of asbestos are now known to be related primarily to four factors: (1) a length greater than 5–15 μm, as below this size the fibre can be easily cleared by lung macrophages; (2) a diameter less than about 3 μm, allowing the fibre to be inhaled to the gas-exchanging part of the lung (asbestos fibres with length > 5 μm and diameter < 3 μm are termed ‘regulated’); (3) insolubility in the lung milieu; and (4) a sufficient dose to the target organ. The mechanism that leads to lung cancer appears to be frustrated phagocytosis, whereby the macrophage is injured in an attempt to engulf long fibres and releases cytokines, mitogens and oxidants that initiate the process of fibrosis and carcinogenesis (Seaton et al., 2010).

The results of the epidemiological, in vitro and in vivo cohort studies indicate that exposure, via inhalation of asbestos minerals, causes lung diseases, in particular the following (Skinner et al., 1988; Dilek and Newcomb, 2003):

Asbestos was declared a proven human carcinogen by the US Environmental Protection Agency, the International Agency for Research on cancer (IARC) of the World Health Organization, and the National Toxicology Program more than 20 years ago (Nicholson, 1986; IARC, 1977, 1988; Collegium Ramazzini, 2010). The global scientific community agrees that there is no evidence of a threshold level of exposure to asbestos fibres below which there is no risk of mesothelioma (Collegium Ramazzini, 2010). From the late 1980s, many countries worldwide began to ban or restrict the use of ACMs in response to the pressure of a large part of the scientific community, asbestos victims’ associations, environmental protection groups and many political parties.

In 1989, the United States Environmental Protection Agency (EPA) issued the Asbestos Ban and Phase Out Rule which was subsequently overturned in the case of Corrosion Proof Fittings v. EPA, 947 F.2d 1201 (5th Cir. 1991). This ruling leaves out many consumer products that can still legally contain trace amounts of asbestos. A complete ban on asbestos-containing material in Australia was introduced in 1991, although some building materials in storage were still being used in the years that followed. In the United Kingdom, blue and brown asbestos were banned in 1985. The ban included also white asbestos in 1999. According to the regulation, importation, supply and use of all forms of asbestos is prohibited. This also comprises second-hand use of asbestos products such as asbestos cement sheets and asbestos boards and tiles including panels which have been covered with paint or textured plaster containing asbestos.

Asbestos has been banned in Italy since 1992 (Law no. 257 issued on 27 March 1992). Since 1997, asbestos has been banned in France by Decree no. 96-1133 issued on 24 December 1996. On 26 July 1999 a document updated Annex 1 of Directive 76/769/EEC on dangerous substances and preparations and proclaimed the end to the use of asbestos throughout all member states of the European Union (EU). Recently, chrysotile asbestos has been included in the list of chemicals in Annex III of the Rotterdam Convention.

If asbestos minerals are considered carcinogenic substances, why is their use restricted or banned in only 55 of 195 countries (28%) in the world and still exploited and used in the remaining countries? The answer is still a matter of controversy and raises a global issue still far from being worked out. The pro-asbestos side claims that only amphibole asbestos minerals are carcinogens whereas chrysotile asbestos is not. This is the so-called amphibole hypothesis which is based on the assumption that chrysotile asbestos has little potential for provoking mesothelioma (see, for example, Liddell et al., 1997; McDonald et al., 1997; Camus, 2001) and that lung diseases are actually due to amphibole minerals (especially tremolite) which are likely to contaminate chrysotile asbestos.

The amphibole hypothesis is supported by knowledge of chrysotile and amphibole behaviour in the lungs. Chrysotile dissolves quickly (low bio-durability) in the lung fluids (especially in the macrophage environment at pH = 4) whereas amphiboles are much more durable (high biodurability) and remain in the lungs for a very long time (Hume and Rimstidt, 1992; Bernstein et al., 2008; Oze and Solt, 2010). Although the position is not shared by the overall scientific community (see, for example, Stayner et al., 1996; Hodgson and Darnton, 2000; Berman and Crump, 2008), there are few studies in which dose–response relationships have been estimated separately for cancer risk and exposure to different fibre types in the same exposed population and this somehow leaves the issue open to debate. Wagner (1997) claims that no mesotheliomas have been reported to have occurred in chrysotile-exposed workers, unless the exposure has been intense and for more than 20 years. This author claims that there must be tremolite contamination of the chrysotile and that a prolonged exposure to large quantities of fibres is a situation that rarely exists today. For these reasons, today 72% of the countries worldwide ban only amphibole asbestos species whereas the use of chrysotile asbestos is permitted with its exposure controlled by technology or by regulations of work practices.

A further source of argument comes from the asbestos substitute materials. Chrysotile substitutes include p-aramid, polyvinyl alcohol (PVA), cellulose, polyacrylonitrile, glass fibres, graphite, polytetrafluoroethylene, ceramic fibres and SiC whiskers. There are reasons to doubt the safety of these substitutes (Camus, 2001). Actually glass and ceramic fibres, SiC whiskers, and rock and slag wools have been classified as possible or probable carcinogens by IARC (Camus, 2001). PVA and p-aramid fibres are less respirable but more biopersistent than chrysotile. P-aramid fibres have induced fibrosis and mesothelioma in inoculation studies (Friedmann et al., 1990). Cellulose displays cytotoxic effects (Huuskonen et al., 1998).

In this scenario of global uncertainty, one side of world’s countries calls for a global ban on all asbestos minerals whereas the other side calls for the dismissal of the ban on asbestos and the controlled use of chrysotile in high-density products, provided that permissible maximum exposure limits of 1.0 fibres/cm³ are respected (recommendations of WHO Group of Experts).

7.4 Use of asbestos in building materials

ACMs are generally divided into two classes: friable asbestos and compact or non-friable asbestos. Friable asbestos refers to any ACM that when dry, can be easily crumbled or pulverized to powder. In practice, free asbestos fibres can easily be scratched off the surface of friable ACM by hand. Virtually any friable asbestos material (with more than 1 wt% asbestos) is considered to be Regulated Asbestos-Containing Material (RACM). Usually, friable asbestos is composed of 70–95 wt% chrysotile and/or amphibole asbestos fibres. A few examples of products of friable asbestos are acoustic ceilings, tiles, plasters and wallboard. Compact asbestos is by definition a composite material in which chrysotile and/or amphibole asbestos fibres are compacted or cemented in a cement or polymeric matrix. The most noteworthy example of compact asbestos material is asbestos-cement in which 4–15 wt% chrysotile and generally 0–5 wt% amphibole asbestos fibres reinforce an ordinary cement matrix. Compact asbestos does not tend to release fibres, unless it is sawn or scratched by mechanical tools (e.g. a chisel).

As discussed in the previous section, the use of asbestos in new construction projects has been banned in many developed countries. In the United States building materials containing asbestos such as asbestos-cement pipes continue to be used in construction. Prior to the ban, asbestos was widely used in building materials. Consequently, many old buildings all over the world still contain asbestos.

Chrysotile has been used more than any other asbestos species and is still by far the most used one (94% of the world’s production). The largest user of chrysotile fibres is the asbestos-cement industry, accounting for about 85% of the total use. For the reasons discussed in section 7.3, chrysotile is probably the only asbestos species that will be used in the future. It is estimated that more than 95% of the commercially developed asbestos ore deposits are chrysotile asbestos (Ross et al., 2008). Due to its availability, some countries have used amphibole species in place of chrysotile in many applications. Friable asbestos is made of nearly pure asbestos fibres, whereas asbestos fibres are diluted in compact composite products (Becklake et al., 2007; D’Orsi, 2007; Virta, 2006; Health and Safety Executive, 2011).

In building materials, friable asbestos has been used in the following applications:

In building materials, compact asbestos has been used in

ACMs in house building materials are illustrated in Fig. 7.4.

Leading developing countries such as China and Russia have continued the widespread use of asbestos. The most common ACM is corrugated asbestos-cement sheets for roofing and side walls. As discussed in section 7.2, the countries where asbestos is banned use man-made mineral fibres (MMMF) or man-made vitreous fibres (MMVF) as substitutes in building materials. The most common commercial asbestos substitute MMMFs are produced from a liquid melt of the starting raw materials by mechanical drawing, blowing with hot gases, and centrifuging as fiberizing methods (Klingholtz, 1977). The most common products are rock/slag wool, which is a furnace product of molten rock, generally a basalt, formed at a temperature of about 1500–1600 °C (De Vuyst et al., 1995; Öhberg, 1987). The maximum working temperature of rock wool is around 750 °C. Glass wool is a furnace product of sand and glass slag rich in alkalis and boron and molten at 1000–1200 °C. The maximum working temperature of glass wool is around 230 °C.

Refractory (ceramic) fibres are synthetic blends of refractory oxides such as alumina and silica molten at 1600–2000 °C with maximum working temperature in the range 1250–1600 °C. They are resistant to chemicals and thermal shock, are light in weight, are sound absorbers, and provide a low thermal conductivity. The major difference between synthetic fibres and asbestos is the fibre morphology. Synthetic fibres invariably display an inflexible habit with a relatively large diameter (1–15 μm) and do not split longitudinally into fibrils but may break transversely into shorter segments. Rock and glass wool replace asbestos as friable insulating material. They can also be used together with an active binder to manufacture sheets and panels to insulate flat surfaces such as cavity walls, wall and ceiling panels, air conditioning ducts and panels, pipes and acoustic frames. They replace asbestos in fireproofing spray and fire door interiors, duplex filler and covering, flat-boards/tiles, acoustic panels and finishes, fireboards, panels on access hatches to service risers and lining service risers and floors, insulation of oil and coal furnaces, insulation and covering of ventilation and air conditioning systems, refrigerators/freezers, clothes dryers, insulation of electrical wires and panels, lagging (steam pipes, boilers, pipework, calorifiers), machine room ceilings, floors, ducts and walls, soundproofing or decorative spray coatings or roofing felt for ceilings, walls, horizontal or vertical beams and columns.

Highly refractory ceramic fibres are especially used for the manufacture of refractory furnace elements such as bricks. They are well used as loose fibres for thermal and/or acoustic insulation and fireproofing in felts, vacuum forming boards/panels/tiles, special papers, textiles, high-temperature adhesives, insulation of oil and coal furnaces, insulation and covering of ventilation and air conditioning systems, refrigerators/freezers, and lagging (International Program on Chemical Safety, 1988).

Asbestos-cement has been substituted by ecological fibre-cement (Bentur and Akers, 1989; Van Zijl and Wittmann, 2010) which contains organic polymers like cellulose [(C₆H₁₀O₅)_n] or polyvinyl alcohol [(C₂H₄O)_x] or recycled materials (Savastano et al., 2005) in place of asbestos fibres.

7.5 The reclamation of asbestos

There are three major steps in the site analysis for the elimination of asbestos in buildings. The first step is the assessment of the presence and nature of asbestos in the building material. The second step is the evaluation of the degree of integrity of the ACM. The third step is the choice of the best reclamation method suitable for that specific case. There are different reclamation techniques which will be discussed in this section.

In general, if the presence of asbestos fibres is suspected, the best way to make a decision about removal is to request a consultancy to a licensed asbestos inspector. The inspector usually identifies the ACMs in the home and determines their friability. Samples of these materials are collected to verify the presence of asbestos fibres. In addition, air samples are collected in order to reveal any environmental exposure to airborne asbestos fibres.

Based on the results of these analyses, the risk of fibre release from the materials is assessed (www.asbestos.com).

Different countries apply different quantitative indicators for the assessment of the exposure limits to asbestos fibres in indoor environments and set different threshold limits of fibre concentration that impose the reclamation of the ACM. There are two different approaches: a direct measurement for the indoor environment and an indirect evaluation for the outdoor environment. For the indoor environment, the threshold limits consider the concentration of fibres in air (generally ff/l = fibres per litre). For the outdoor environment, the assessment considers the degree of integrity of the ACM, namely, whether the ACM is prone to release asbestos fibres in the environment. In 1987, the World Health Organization (WHO) fixed limiting values of 1 ff/l and 0.5 ff/l if scanning electron microscopy (SEM) and optical microscopy, respectively, are used for the determination of fibre concentration (Cecchetti et al., 2005). The Italian law (Italian D.M. 06/09/1994) compels the reclamation of the ACM in the indoor environment whenever the fibre concentration is > 20 ff/l if measured with phase contrast optical microscopy (PCOM) or > 2 ff/l if measured with SEM. In outdoor environments, reclamation of the ACM is mandatory if more than 10% of the total exposed area of the ACM has deteriorated (Italian D.M. 06/09/1994). There are attempts to establish a direct evaluation even for outdoor environments but the issue remains open (Gualtieri et al., 2009b). One indication is provided by the State of California that established, in Proposition nr. 65, a concentration level of 100 ff/day (hypothetically 0.005 ff/l) as the risk threshold (Minoia et al., 1997). The US Environmental Protection Agency has established that the probability of developing cancer (mesothelioma) is 1:10⁶ if the individual was to continuously breathe air with an average asbestos concentration of 0.004 ff/l for their entire life. This probability increases if the concentration increases (0.04 ff/l → 1:10⁵, 0.4 ff/l → 1:10⁴, etc.). In Italy, the threshold for ambient asbestos concentration in an environment where removal work is under way (work environment) is 50 ff/l for a day’s exposure. A suggested concentration limit for outdoor living environments may be 0.1 ff/l determined by SEM or transmission electron microscopy (TEM) (Gualtieri et al., 2009b).

Current opinion considers that ACMs in good conditions do not represent a priority risk and that the reclamation event causes much more fibre dispersion in the environment than the long-term fibre release during the entire life of the ACM itself. On the other hand, although ACMs in good conditions may not represent an immediate priority risk, as potential source of asbestos fibre dispersion they certainly persist as quiescent hazard. As a matter of fact, fibre dispersion may arise due to natural events (floods, earthquakes, thunderstorms) or human-induced catastrophic events (e.g. vandalism). A well-known example is the crime against humankind committed on 11 September 2001. More than 1000 t of asbestos are thought to have been released into the air during the destruction of the Twin Towers (Nolan et al., 2005). Many thousands of people are now thought to be at risk of developing cancer due to this exposure. For these reasons, in many countries ACMs are being progressively removed from the environment regardless of their conditions.

ACMs (namely asbestos-cement roofing) reclamation techniques in outdoor environments can be classified as follows (Gualtieri, 2000):

Abatement is the most common reclamation technique as it has the advantage that the asbestos fibres are totally removed from the reclamation site after the operation (Fig. 7.6). It has some disadvantages such as the production of toxic refuse, risks of exposure for removal workers, and risk of environmental pollution during and after the operation. These disadvantages are partly circumvented when in situ techniques are applied. However, asbestos is still present in situ and the status of the reclaimed site should be periodically monitored following an inspection and maintenance programme.

The methods for ACM reclamation in indoor environments are analogous to those applied in outdoor environments. They can be classified as follows (Gualtieri, 2000):

Although the reclamation methods for outdoor and indoor environments are basically identical, there are major differences in the application of the methods. In both cases, during the recovery operations, workers are obliged to wear head-to-toe protection such as overalls and a high-efficiency particulate air (HEPA P3) respirator (see Fig. 7.7). In direct contrast to outdoor intervention, indoor building reclamation sites must be efficiently sealed. The static confinement is obtained by dividing the area into smaller lots separated by temporary rigid gypsum boards or panels. All the doors and windows should be sealed and protected using polyethylene wraps. All the openings and sockets, air-conditioning systems and others should be sealed. Fissures and holes in the walls should be sealed off with silicone paste or expanding foams. Dynamic containment is also applied by negative air pressure units to keep the building recovery site in negative pressure with respect to the external areas so as to prevent the release of fibres outside the containment area (D’Orsi, 2007). The pressure difference between the containment area and the external areas should be around 0.3–0.9 psi. According to D’Orsi (2007), air extracted by the pumping system should be filtered using high-efficiency HEPA filters (99.97 DOP). Access to the abatement area is possible exclusively through the so-called decontamination units or decon units. These units must always be constructed and operational prior to the preparation of the building reclamation site. They shall be fully framed. Once the framework is in place, the inside of the unit is required to be wrapped with polyethylene sheeting.

A common worker decon unit consists of three successive rooms: a clean room, a shower room and an equipment room. Each room is separated by curtain doorways and airlocks on each side of the shower room. No asbestos contaminated items shall be found in the clean room. Workers use this area to remove clothes and personal belongings and to wear protective clothing and respirators. Workers move to the shower room on their way into the work area. On the way out of the contaminated work area, workers leave the equipment room and all contaminated clothes behind and enter the shower area with the respirator still on. The equipment room is a contaminated area where all of the equipment is stored after the reclamation operations. Here, the worker removes the disposable suit and places it in a properly labelled polyethylene disposal bag or lined container (Cecchetti et al., 2005). A special decontamination unit is used to allow passage of the removed ACM to be disposed from the work area during the abatement activities.

The ACM decontamination unit consists of three rooms: a washing room where the sealed polyethylene bags with the removed ACM are washed; a packing room where the washed polyethylene bags with the removed ACM are packed into another polyethylene bag and finally sealed off with suitable adhesive paper; and a storage room where all the double-sacked bags are stored waiting to be moved out to the external disposal area (D’Orsi, 2007). Before it is pumped off to the drainage system, the water used for washing the bags in the first room is filtered through MgO-rich filters.

When ACMs are removed from the environment, hazardous wastes are produced. Their destiny is an important environmental issue. There are nowadays two possible ways to dispose of ACMs:

The next section discusses the advantages and disadvantages of both these methods.

7.6 The disposal of asbestos-containing materials (ACMs) and recycling

In the countries where asbestos is banned and reclamation policies are adopted, removed ACM is usually disposed of as hazardous waste in specially committed landfills. The use of inactive mines such as open pit mines and underground mines as disposal sites for ACM wastes is common all over the world, and especially in Europe (Austria, France, Germany, Italy, Slovenia, Sweden, Switzerland, United Kingdom, and others). In Germany, underground mines such as salt and iron mines have been used for the deposition of waste including ACM (Gidarakos et al., 2008). Landfill cannot be regarded as the ultimate solution for the disposal of ACM, as a zero risk of fibre dispersion in air and water cannot be guaranteed. Fibre dispersion during disposal operations may occur because, although the sealed packages of ACM should be handled with great care, avoiding any possible breakage of the packages or contact with water, the opposite is frequently observed in the real case (see Fig. 7.8). Fibre dispersion in the leachate occurs in the medium to long term. The polyethylene packages decompose with time and water solutions percolating through the asbestos-cement slates slowly dissolve the cement matrix and prompt the release of the fibres which concentrate in the leachate itself (Paglietti et al., 2002). Hence, in the long term, the landfill should no longer be considered a closed system and hypothetically leachate should be collected and disposed of as hazardous waste forever.

Preference for material recycling instead of landfill dumping has been included in the recent Directive 2008/98/EC of 19 November 2008 on waste and repealing certain Directives. An alternative solution to landfill disposal of ACM is the thermal transformation into supposedly non-hazardous products, and safe recycling of the transformation product as secondary raw material. This process relies upon the well-documented scientific evidence that the asbestos minerals are transformed into stable silicates at high temperature (Martin, 1977; MacKenzie and Meinhold, 1994; Cattaneo et al., 2003; Gualtieri and Tartaglia, 2000; Gualtieri et al., 2008a, 2008b). Chrysotile asbestos between 700 and 800 °C undergoes dehydroxylation and subsequent recrystallization which leads to the later formation of forsterite and enstatite: at equilibrium

The result of the solid-state recrystallization of a chrysotile fibre is shown in the TEM image displayed in Fig. 7.9. Crocidolite asbestos at 1100 °C shows a more complex reaction path which involves iron oxidation (Gualtieri et al., 2004):

The importance of transforming and recycling ACM is witnessed by the existence of a huge number of research (laboratory and pilot) projects and patents – see, for example, the CORDIAM project for the production of cordierite refractories by Abruzzese et al. (1998), the Asbestex process (Johannes, 2003), the A.R.I. process (Downey and Timmons, 2005), the KRYAS process (Gualtieri et al., 2008a), the GeoMelt process (Finucane et al., 2008), and many others which employ for example mechanochemical treatments (Plescia et al., 2003), microwaves (Leonelli et al., 2006), or Joule heating vitrification (Dellisanti et al., 2009). Among these, at the moment only the INERTAM process (Borderes, 2000) has been successfully converted into a fixed large-scale industrial plant that has been operating for more than 10 years in Morcenx (France).

The challenge concerning the transformed ACMs is to find suitable and attractive recycling solutions. Recently, it was demonstrated that the product of transformation of asbestos-cement can be successfully recycled in the production of traditional ceramics (Gualtieri et al., 2008a), clay bricks, glasses, glass-ceramics, ceramic frits, ceramic pigments and plastic materials (Gualtieri et al., 2010). The recycling of up to 20 wt% of thermally treated asbestos-cement for the production of concrete has also been successfully attained (Gualtieri and Boccaletti, 2011). Because it is mainly composed of calcium and silica, the use of this secondary raw material as a CO₂-free source of Ca in place of calcium carbonates, for example in the production of clinker or concrete, is welcomed in view of a reduction of the CO₂ emissions during the industrial manufacturing processes.

7.7 Conclusion and future trends

The next years of this millennium will hopefully witness the solution of the global issue of asbestos. Undisputed results from toxicological tests on pure and well-characterized natural fibres and epidemiological studies should finally assess whether or not the ban on chrysotile asbestos is supported by scientific evidence and whether it is recommended to continue or ban the use of ACMs in building materials. The extensive use of chrysotile asbestos prompted the discovery of new outstanding applications for catalysis, production of silica fibres and non-linear optics (Silva and Jesus, 2003; Wang et al., 2006; Bardosova et al., 2007). However, in the countries where asbestos is banned, new solutions and new materials to be used as asbestos substitute materials are proposed. An outstanding result is the so-called nano-chrysotile synthesized by an Italian group (Falini et al., 2004). The determination of the potential toxicity of fibres other than asbestos widely used as building materials is another challenging field of research. It is legitimate to ask whether asbestos-like minerals such as sepiolite (Bellmann et al., 1997) are safe.

In a world that shares the policy of recycling, it seems unwise to simply dump ACMs in landfills. Innovative technological solutions now exist to convert and recycle ACMs as secondary raw materials and turn the problem into a new source for building materials such as concrete (Gualtieri and Boccaletti, 2011). It is an economic and social opportunity not to be missed. Recycling of ACMs in building materials has the potential to save primary raw materials and decrease the overall emissions of CO₂. New technologies for the transformation and recycling of ACMs have been recently elaborated, and the development of large-scale plants is expected in a few years.

7.9 References

7.8 Sources of further information and advice